1. Field of the Invention
The present invention relates to an equipment and a method for cleaning and drying a substrate. More particularly, the present invention relates to an equipment and a method for cleaning and drying various substrates such as a semiconductor substrate in semiconductor device manufacturing steps, a reticle (photomask) in a lithography step as one of the semiconductor device manufacturing steps, a flat panel in liquid crystal display manufacturing steps, etc.
2. Description of the Related Art
In order to clean the surface of the semiconductor substrate on which semiconductor devices are formed, etc., the cleaning step of the semiconductor substrate and the drying step following to the cleaning step are frequently repeated in the semiconductor device manufacturing steps. Especially, in order to form a silicon oxide film of high quality, it is essential to implement a ultra clean surface on the surface of the semiconductor substrate. Therefore, an oxide film on the surface of the semiconductor substrate is removed before the oxidizing step so as to expose the ultra clean surface.
Normally, the method of etching the surface of the semiconductor substrate by using a hydrogen fluoride group acid has been widely used as the method of removing the oxide film. An important matter in this hydrogen fluoride process is how to remove the moisture stuck on the semiconductor substrate when the semiconductor substrate is dried after cleaning. Usually, as the drying method after cleaning, the spin drying such as spin dryer, rinser dryer, etc. has been employed. In the spin drying, the semiconductor substrate is dried by rotating the semiconductor substrate at a high speed to blow off the moisture on the surface by the centrifugal force. However, if the spin drying is employed after the hydrogen fluoride process, often spot-like foreign matters, each of which is called a water mark, are generated on the surface of the semiconductor substrate. It has been known that such water mark is a stain caused by a waterdrop, which remains or is stuck onto the semiconductor substrate being cleaned/dried, and is formed of silica group material. This water mark acts as a mask in the etching process performed after the water mark has been generated, and thus makes it difficult to control the etching process. In addition, since the silica group material is formed of insulative silicon dioxide, it causes defects of conduction of the contact portion if it generates on the contact portions.
In recent years, in order to prevent generation of the water mark, the steam drying using 2-propanol or isopropyl alcohol (abbreviated as "IPA" hereinafter) is being employed. According this method, the moisture on the semiconductor substrate is replaced with the IPA steam by exposing the semiconductor substrate to the IPA steam, and then drying of the semiconductor substrate is conducted by evaporating naturally the replaced IPA. In the prior art, as the cleaning/drying equipment employing this steam drying, for example, followings are listed.
FIG. 1 is a schematic view showing an example of a configuration of a substrate cleaning/drying equipment using the steam drying. As shown in FIG. 1, the substrate cleaning/drying equipment comprises a cleaning chamber 5, and a drying chamber 13. The cleaning chamber 5 may be composed of a single chamber which can switch various chemicals such as hydrogen fluoride, etc. and the ultra pure water continuously, or composed of a plurality of chemicals chambers and a rinsing chamber. An IPA temperature adjusting tub 7 in which the IPA is filled, and a heater 9 for heating the IPA temperature adjusting tub 7 to boil the IPA in the IPA temperature adjusting tub 7 are provided in the drying chamber 13. The IPA steam 11 is filled in an upper area of the drying chamber 13.
An operation of the substrate cleaning/drying equipment shown in FIG. 1 is given as follows. To begin with, a cassette 3 on which a plurality sheets of semiconductor substrates 1 are loaded is immersed into the cleaning chamber 5 to effect the cleaning by using various chemicals and the ultra pure water. Then, a predetermined carrying means carries the cassette 3 into the drying chamber 13 after the cleaning. Then, the semiconductor substrates 1 in the cassette 3 are left in the IPA steam 11, then the moisture stuck on the semiconductor substrates 1 is replaced with the IPA steam, and then the semiconductor substrates 1 are dried by naturally evaporating the replaced IPA. In this manner, according to the substrate cleaning/drying equipment using the IPA steam drying shown in FIG. 1, the moisture on the semiconductor substrates 1 can be removed completely, so that generation of the water mark can be prevented.
As described above, in the substrate cleaning/drying equipment shown in FIG. 1, since the cleaning chamber 5 and the drying chamber 13 are provided separately, transfer of the semiconductor substrates 1 from the cleaning chamber 5 to the drying chamber 13 is needed after the cleaning has been terminated. In this transfer, the semiconductor substrates 1 are exposed to the outer air, but natural drying of the semiconductor substrates 1 will occur during transfer according to transfer velocity, transfer distance, etc. This natural drying causes the water marks on the surface of the semiconductor substrates 1. In contrast, the IPA steam is generated by boiling directly the IPA in the drying chamber 13. Therefore, a great deal of IPA must be consumed and also an enough safety countermeasure against the flammability of the IPA must be taken.
As the substrate cleaning/drying equipment which can avoid the above problem, for example, the following has been proposed. FIG. 2 is a schematic view showing another example of a configuration of a substrate cleaning/drying equipment using a steam drying. This substrate cleaning/drying equipment is constructed such that cleaning and drying of the semiconductor substrates are carried out in the same chamber. As shown in FIG. 2, this substrate cleaning/drying equipment has a cleaning/drying chamber 15 in which both cleaning and drying of the semiconductor substrates 1 are executed. The cleaning/drying chamber 15 has a cleaning tub 17 at its bottom. The cleaning tub 17 may be composed of a single processing tub which can switch various chemicals such as hydrogen fluoride, etc. and the ultra pure water continuously, or composed of a plurality of chemicals tubs and a rinsing tub. The IPA steam 11 is filled in an upper area of the cleaning/drying chamber 15. The IPA steam 11 is generated in an IPA temperature adjusting tub 21 which is arranged on the outside of the cleaning/drying chamber 15. Then, a carrier gas such as N.sub.2, Ar, etc. acting as the temperature adjusting gas is introduced into the IPA temperature adjusting tub 21. The IPA steam 11 in concert with the carrier gas is introduced from the IPA temperature adjusting tub 21 into the cleaning/drying chamber 15 via the IPA steam pipe 19.
An operation of the substrate cleaning/drying equipment shown in FIG. 2 is given as follows. At first, the cassette 3 on which a plurality sheets of semiconductor substrates 1 are loaded is immersed into the cleaning tub 17 to execute the cleaning by using various chemicals and the ultra pure water. Then, after the cleaning has been finished, the IPA steam 11 is introduced into the cleaning/drying chamber 15 such that an upper area of the cleaning/drying chamber 15 is filled with the IPA steam 11. Then, the IPA steam 11 spreads on the surface of the ultra pure water in the cleaning tub 17 to form an IPA condensed layer. Thereafter, the semiconductor substrates 1 is pulled up gradually from the ultra pure water into the IPA steam 11. At that time, the ultra pure water stuck on the semiconductor substrates 1 is replaced with the condensed IPA, and then the semiconductor substrates 1 are dried by naturally evaporating the replaced IPA. In this manner, the cleaning and drying of the semiconductor substrates 1 can carried out in the same chamber in the substrate cleaning/drying equipment shown in FIG. 2. That is to say, transfer of the semiconductor substrates 1 from the cleaning step to the drying step in the outer air can be omitted. Accordingly, unlike the equipment in FIG. 1, natural drying of the semiconductor substrates 1 during transfer does not occur and thus no water mark is generated. Further, in the substrate cleaning/drying equipment in FIG. 2, since the IPA steam 11 is introduced into the cleaning/drying chamber 15 only at the time of drying the semiconductor substrates 1, consumption of the IPA can be suppressed inevitably. Furthermore, since the IPA is not heated in the cleaning/drying chamber 15, the safety against flammability of the IPA can be assured sufficiently.
However, the substrate cleaning/drying equipment shown in FIG. 2 has a following disadvantage. FIG. 3 is a conceptional view showing the case where the semiconductor substrate 1 showing in FIG. 2 is pulled up from the ultra pure water 23 in the cleaning tub 17 into the IPA steam 11. As shown in FIG. 3, silica group material 25, which is stuck on the semiconductor substrate 1 after the hydrogen fluoride process, can be removed from the semiconductor substrate 1 because of difference in the surface tension acting to the ultra pure water 23 and the IPA condensed layer when the semiconductor substrate 1 is pulled up from the ultra pure water 23 in the IPA steam 11. In the meanwhile, the batch process in which a plurality of semiconductor substrates are processed at once is commonly employed in the existing cleaning step. The semiconductor substrates 1 are arranged so as to oppose their front surfaces to their back surfaces mutually. Accordingly, there is a possibility that silica group material 25 being removed once moves on the surface of the ultra pure water 23 and then sticks onto the surface of the opposing semiconductor substrate 1 again. In particular, an oxide film formed in various steps still remains on the back surface of the semiconductor substrate 1, so that the oxide film is subjected to the hydrogen fluoride process to thus generate the silica group material 25. Therefore, such silica group material 25 may be stuck once again on the surface of the semiconductor substrate 1, i.e., the surface on which the semiconductor devices are formed, to thus cause particles. In addition, if both the oxide film and the silicon are exposed on the surface of the semiconductor substrate 1, re-sticking of the silica group material 25 becomes remarkable owing to difference in wettability of the oxide film and the silicon.
Moreover, with the higher integration density and higher density of the recent semiconductor devices, unevenness on the semiconductor substrate 1 tends to be enhanced extremely. As a result, re-sticking of the silica group material as shown in FIG. 3 an be similarly caused between such unevennesses.